So-called bag-in-box containers are already well known for still table wine. Such a container consists of a substantially impermeable bag, usually of metalised polyester, disposed within a box of cardboard or similar material, the bag being filled with wine and having a tap projecting through the box material so that the wine can be easily dispensed. The great advantage of such a container over a conventional bottle, carafe or the like is that the bag is made of flexible material so that as liquid is dispensed the bag collapses by a corresponding amount and no air is allowed to enter to cause oxidation of the liquid. Progressive oxidation of a beverage such as wine leads, of course, to the beverage firstly becoming stale and subsequently spoiled. Accordingly the bag-in-box packaging keeps the product fresh for an extended period.
A further advantage of bag-in-box containers is that they are lighter than most conventional containers and are therefore more suitable for transporting liquids and/or for holding larger quantities of liquid. The integral tap is also particularly convenient for dispensing the contained liquid and there is no difficulty in the consumer opening the container.
It is desirable to extend bag-in-box packaging to pressurised liquids, particularly carbonated beverages such as beer and soft drinks, so as to achieve, in relation to these liquids, the above-mentioned advantages. However, when such liquids are filled into flexible bags within semi-rigid casings in the form of boxes, the latter have been found to sag or bulge outwardly because of the pressure within the liquid. This is clearly unsatisfactorily as it makes the overall container unstable and likely to topple over and it is not possible to stack the containers for storage or transportation.